Ultrasonic imaging catheter

ABSTRACT

An ultrasonic imaging catheter apparatus and a method of using the same to scan the inner wall of a body lumen. The ultrasonic imaging catheter apparatus comprises: (a) a flexible elongate element adapted for insertion into a body lumen, the elongate element having distal and proximal ends; (b) an ultrasonic transducer generating and detecting ultrasonic energy disposed proximate the distal end of the elongate element; (c) a reflective member disposed proximate the ultrasonic transducer and optionally rotatable with respect to an axis of the body lumen, wherein the reflective member is adapted to reflect (i) ultrasonic energy generated by the ultrasonic transducer to a wall of the body lumen and (ii) ultrasonic energy reflected by the wall back to the transducer; and (d) an actuator, for example, an electroactive polymer actuator, adapted to change the angle of incidence of the ultrasonic energy relative to the reflective member.

STATEMENT OF RELATED APPLICATION

This patent application is a continuation of application U.S. Ser. No.10/631,872, filed Jul. 31, 2003, entitled “Ultrasonic Imaging Catheter,”which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to catheters appropriate for imaging, and moreparticularly to catheters appropriate for intravascular ultrasonographicimaging applications.

BACKGROUND OF THE INVENTION

Intravascular ultrasound (IVUS) catheters and methods for imaging areknown. For example, U.S. Pat. No. 5,000,185 to Yock, the entiredisclosure of which is incorporated by reference, discloses devices andmethods for high-resolution intravascular ultrasound imaging to assistwith the administration of vascular interventional therapy and tomonitor the results of such therapy. In Yock, an ultrasonic transduceris carried by the distal end of a catheter adapted for insertion into ablood vessel, whereupon either the transducer or another element, suchas an ultrasound mirror, is rotated and/or translated relative to thecatheter to image different portions of the vessel.

In spite of advances in the art, however, there continues to be a needfor a catheter apparatus that can provide longitudinal scans of a vesselsurface along the axis of the vessel, and oblique scans which examinevessel regions distal of the catheter tip, without the need for anaccompanying longitudinal movement of the transducer or other catheterelement along vessel axis.

SUMMARY OF THE INVENTION

The above and other needs of the prior art are addressed by the presentinvention. According to an embodiment of the present invention, anultrasonic imaging catheter apparatus is provided, which comprises thefollowing: (a) a flexible elongate body adapted for insertion into abody lumen, the elongate body having distal and proximal ends; (b) anultrasonic transducer generating and detecting ultrasonic energydisposed proximate the distal end of the elongate body; (c) a reflectivemember disposed proximate the ultrasonic transducer and which isoptionally rotatable with respect to an axis of the body lumen, whereinthe reflective member is adapted to reflect (i) ultrasonic energygenerated by the ultrasonic transducer to a wall of the body lumen and(ii) ultrasonic energy reflected by the wall back to the transducer; and(d) an actuator, such as an electroactive polymer actuator, theelectroactive polymer actuator being adapted to electronically controlthe tilt of the reflector and thus the angle of incidence of theultrasonic energy upon the reflective member.

Where used in connection with the present invention, the electroactivepolymer actuators typically comprise an electroactive polymer region, acounter-electrode region, and an electrolyte-containing region disposedbetween the electroactive polymer region and the counter-electroderegion. Beneficial electroactive polymers for these embodiments includepolyaniline, polysulfone, polyacetylene and polypyrrole.

In some embodiments, the control signals for the ultrasonic transducerand for the electroactive polymer actuator are transmitted via a sharedsingle electrical conduction path, for example a coaxial cable. In suchembodiments, it is beneficial to provide the ultrasonic transducer witha high pass filter to block passage of low-frequency/dc electroactivepolymer actuator control signals, and to provide the electroactivepolymer actuator with a low pass filter to block passage ofhigh-frequency ultrasonic transducer control signals.

The entire catheter assembly, including the reflective member,transducer and electroactive polymer, are rotated in some embodiments.In these and other embodiments, the catheter apparatus can furthercomprise a motor and a drive shaft for translating torque from themotor, for example, through a suitable connector or rotary joint,thereby rotating the reflective member, among other elements.

Other aspects of the present invention are directed to methods ofscanning the inner wall of a body lumen. These methods comprise: (a)providing a catheter apparatus like that above; (b) sweeping theultrasonic energy from the transducer in a pattern over the interiorwall of the body lumen by operating the electroactive polymer actuatorto change the angle of incidence of the ultrasonic energy upon thereflective member, and by optionally rotating the reflective member; (c)receiving ultrasonic energy reflected from the interior wall of the bodylumen; and (d) producing an image from the reflected ultrasonic energy.For example, the ultrasonic energy can be directed at a forward anglebetween about 10° to about 85° relative to the axis of the body lumen,such that a conical forward sweep is performed.

One advantage of the present invention is that catheters, systems andmethods are provided for intravascular ultrasonography.

Another advantage of the present invention is that catheters forintravascular ultrasonography are provided, in which the wall of anadjacent body lumen can be axially (longitudinally) scanned, without theneed for axial movement of the transducer or other element relative tothe body lumen.

Another advantage of the invention is that catheters for intravascularultrasonography are provided, which can provide for forward, lateral andretrograde scanning, without the need for axial movement of thetransducer or other element relative to the body lumen.

Additional embodiments and advantages of the invention will becomereadily apparent to those of ordinary skill in the art upon review ofthe following detailed description in which the preferred embodimentsare set forth in detail.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic partial cross-sectional view of the distal end ofa catheter apparatus, in accordance with an embodiment of the presentinvention. FIG. 1B is a schematic partial cross-sectional view of thedistal end of a catheter apparatus, in accordance with anotherembodiment of the present invention.

FIG. 2 is a schematic top view of the distal portion of FIG. 1A.

FIG. 3 is schematic diagram illustrating three scanning sections, whichcan be generated using a catheter apparatus in accordance with thepresent invention.

FIG. 4 is a schematic block diagram of the electrical componentsutilized in a catheter system, in accordance with an embodiment of thepresent invention.

FIG. 5 is a schematic cross-sectional view of an electroactive polymeractuator useful in connection with the present invention.

FIG. 6 is a schematic cross-sectional view of another electroactivepolymer actuator configuration useful in connection with the presentinvention.

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the present invention are shown. This invention may, however, beembodied in different forms and should not be construed as limited tothe embodiments set forth herein.

Referring now to FIG. 1A, and in accordance with one aspect of thepresent invention, a distal portion of a catheter apparatus 110 isillustrated, which is adapted for insertion into a body lumen, forexample, a blood vessel within the coronary vasculature.

In the embodiment shown, an ultrasonic transducer 132, an associatedultrasonic lens 134, and a reflective member 136 are carried at thedistal end of a flexible shaft of catheter apparatus 110. An electricalsystem (described in more detail below) is connected to the ultrasonictransducer 132 for supplying signals to and receiving signals from thetransducer 132 during operation. The electrical system also suppliessignals to an actuator 140, which is used to change the angle at whichultrasonic waves are incident upon the reflective member 136 duringoperation. The various elements of the catheter apparatus 110 aretypically rotated during operation by means of mechanical torque, whichis transmitted along drive shaft 114.

The ultrasonic transducer 132 can be formed, for example, using any of anumber of materials that are known in the art. For instance, singlecrystals, which are capable of operating at a frequency range of, forexample, 5 to 50 megahertz, are known in the art. Typical materials forforming such crystals include barium titanate or cinnabar. Conductiveelectrodes, for example, films of gold or other conductive metals, maybe provided on opposing surfaces of the crystal. If desired,oscillations from the backside of the crystal can be damped as is knownin the art, for example, through the use of a suitable backing material.Of course, other materials are known besides piezoelectric crystaloscillators for the formation of ultrasonic transducers. For example,organic materials such as polyvinylidene difluoride (PVDF) andvinylidene fluoride-trifluoroethylene copolymers are known, which mayalso be used to form the ultrasonic transducer.

The ultrasonic transducer is also provided with an ultrasonic lens 134,as is known in the art. In the embodiment illustrated in FIG. 1A, theultrasonic transducer 132 is mounted within the end of drive shaft 114,although many other placement locations are clearly possible. Forexample, the ultrasonic transducer 132 can be mounted to housing 116, ifdesired.

A reflective member 136 is also disposed in the catheter apparatus 110.The reflective member 136 can be, for example, an ultrasonographicmirror made, for example, from metal such as stainless steel or a hardpolymer such as polycarbonate with high reflectivity at ultrasoundfrequencies, as is known in the art. Reflective member 136 is disposedwithin the catheter apparatus 110 such that the energy generated by thetransducer 132 is reflected into the tissue of an adjacent body lumen(not shown). Some of this energy will rebound from the lumen tissue, tobe again reflected by the reflective member 136 back to the transducer132.

More particularly, in the configuration illustrated in FIG. 1A, a signalgenerated by the transducer 132 travels axially until is meetsreflective member 136, at which point the signal is deflected at anangle θ₂ from the device axis a (see oblique ray r₀). Note that, in thisembodiment, the angle at which the signal is deflected relative to thedevice axis a is equal to 2 times the angle θ₁ at which the reflectivemember 136 is tilted from the device axis a. For example, by tilting thereflective member 45 degrees from the device axis a (i.e., θ₁=45°, seeposition of reflective member 136 designated by dashed lines), thesignal from the transducer 132 is deflected in a direction orthogonal tothe device axis a (i.e., in a direction where θ₂=90°; see vertical rayrv). By tilting the reflective member to more than 45 degrees from thedevice axis a (i.e., θ₁>45°, not illustrated) the signal from thetransducer 132 will be deflected rearward of the point at which theultrasound energy is incident upon the reflective member 136. The angleof inclination of the reflective member 136 can vary widely, typicallyranging from 10° to 80°, more typically from 10° to 40° relative to theaxis a, thereby providing a forward view.

In the embodiment illustrated in FIG. 1A, the reflective member 136 ismounted distal to the transducer 132. However, alternate embodiments areclearly possible, including those in which the reflective member 136 isprovided at a position that is proximal to the ultrasonic transducer132.

As illustrated in FIG. 1A, catheter apparatus 110 includes a housing 116attached to the end of drive shaft 114. The drive shaft 114 in thisembodiment is of a flexible construction, which allows the catheterapparatus 110 to be guided along tortuous paths, for example, bloodvessels of the coronary, peripheral or cerebral vasculature. The driveshaft 114 is also engineered with sufficient strength to translatemechanical torque along its length and rotate the housing 116 at adesired rotational rate. An example of an appropriate drive shaftmaterial for use in connection with the present invention is acounterwound multifilar structure with good torque fidelity, asdisclosed in U.S. Pat. No. 5,372,138, to Crowley et al, the entiredisclosure of which is incorporated by reference.

In this connection, a motor drive (not shown) is provided in thisembodiment for rotating the drive shaft 114, although manual rotationmay also be employed. By rotating the drive shaft, the transducer signalcan be swept in a desired pattern, providing, for example, a 360°conical scan of the body lumen. As schematically illustrated in FIG. 3,by appropriately tilting the reflective member, the angle of the conicalscan of a body lumen l can be swept, for example, between a forwardconical scan c_(f) to a lateral disc d to a rearward conical scan c_(r).

The housing 116 in the embodiment of FIG. 1A is provided with a cutout116 a (see FIG. 2), which provides an aperture through which ultrasonicenergy can be directed without interference from reflective member 136to a body lumen wall, and back. However, it is also possible to form thehousing 116 of a material that causes minimal attenuation of theultrasonic signal that is transmitted and received by transducer 132.Suitable low-attenuation materials include polyethylene, siliconerubber, polyvinyl chloride, polyurethanes, polyesters, natural rubbers,and the like.

It is frequently beneficial to provide the catheter apparatus 110illustrated in FIG. 1A with within an outer protective sheath. The outerprotective sheath can be formed from a variety of materials, forexample, materials such as those listed in the prior paragraph. Althoughevery element of the catheter assembly 110 illustrated in the embodimentof FIG. 1 a is adapted to rotate en masse, it is desirable in manyembodiments to provide the catheter assembly 110 within an outerprotective sheath that does not rotate, as is known in the art.

A coaxial cable is provided within the drive shaft 114 in the embodimentof FIG. 1A. As is typical, the coaxial cable includes two conductors—acore conductor 122, commonly a wire such as a copper wire, and an outerannular shield or conductor 124, commonly a wire braid such as a copperwire braid. Coaxial cable is advantageous due to the low attenuation andgood electromagnetic shielding associated with the same, particularly athigher frequencies. In the embodiment illustrated, a current path isestablished form the core conductor 122 to the actuator 140 viaconductive line 125, while another current path is established betweenthe annular conductor 124 and the actuator 140 via conductive line 126.

In accordance with the embodiment illustrated, the coaxial conductors122, 124 carry at least two groups of signals. Members of the firstgroup of signals are high frequency signals, which are transmitted toand from the ultrasonic transducer 132. Members of the second group ofsignals are low frequency or dc signals, which are transmitted to theactuator. In this embodiment, it is beneficial to provide a high passfilter, e.g., a simple capacitor blocking 123, to isolate the transducer132 from the low frequency actuator signals. It may also be beneficialto utilize a low pass filter, e.g., a simple inductor (not shown), toisolate the actuator 140 from the high frequency transducer signals.

In FIG. 1A, the housing 116 is provided with an assembly comprising areflective member 136 that is rotatable (i.e., tiltable) about an axisestablished by a mechanical pivot 137, which axis is orthogonal to thelongitudinal axis a of the catheter assembly 110 in the embodimentillustrated. Although a pivot 137 is illustrated, numerous otherconfigurations are possible, including simply mounting the reflectivemember 136 on a member that can be repeatedly flexed as required. Theangle of tilt of the reflective member 136 is adjusted in the embodimentof FIG. 1A using a single actuator 140, although multiple actuators canobviously be employed, if desired.

The actuators used in connection with the endoscopes of the presentinvention are typically electrically controlled actuators (as usedherein, “electrically controlled actuators” include those actuators thatare activated by photons) such as piezoelectric activators, shape memoryactivators and/or electroactive polymer actuators, with actuators basedon electroactive polymers being preferred.

Members of the family of plastics referred to as “conducting polymers,”electroactive polymers are polymers characterized by their ability tochange shape in response to electrical stimulation. They commonlyfeature a conjugated backbone and have the ability to increaseelectrical conductivity under oxidation or reduction.

Some common electroactive polymers are polyaniline, polysulfone,polypyrrole and polyacetylene. Polypyrrole is pictured below:

These materials are typically semi-conductors in their pure form.However, upon oxidation or reduction of the polymer, conductivity isincreased. The oxidation or reduction leads to a charge imbalance that,in turn, results in a flow of ions into the material in order to balancecharge. These ions, or dopants, enter the polymer from an ionicallyconductive electrolyte medium associated with the electroactive polymeror are redistributed within the polymer. The electrolyte may be, forexample, in the form of a gel, a solid, or a liquid. If ions are alreadypresent in the polymer when it is oxidized or reduced, they may exit thepolymer.

It is well known that dimensional changes may be effectuated in certainconducting polymers by the mass transfer of ions into or out of thepolymer. For example, in some conducting polymers, expansion is due toion insertion between chains, whereas in others inter-chain repulsion isthe dominant effect. Regardless of the mechanism, the mass transfer ofions into and out of the material leads to an expansion or contractionof the polymer.

Currently, linear and volumetric dimensional changes on the order of 25%are possible. The stress arising from the dimensional change can be onthe order of 3 MPa, far exceeding that exerted by smooth muscle cells,allowing substantial forces to be exerted by actuators having very smallcross-sections. These characteristics are ideal for construction of thedevices of the present invention.

Referring now to FIG. 5, an electroactive polymer actuator 10 is shownschematically in cross-section. Active member 12 of actuator 10 has asurface coupled with electrolyte 14 and has an axis 11. Active member 12includes an electroactive polymer that contracts or expands in responseto the flow of ions out of, or into, the active member 12. Ions areprovided by electrolyte 14, which adjoins member 12 over at least aportion, and up to the entirety, of the surface of active member 12 inorder to allow for the flow of ions between the two media.

Many geometries are available for the relative disposition of member 12and electrolyte 14. In accordance with some embodiments of theinvention, member 12 may be a film, a group of films, a fiber, a groupof fibers, or a combination of the same disposed so as to actcollectively to apply a force in a longitudinal direction substantiallyalong axis 11 in this instance.

Active member 12 includes an electroactive polymer. Many electroactivepolymers having desirable properties are known to persons of ordinaryskill in the art. In accordance with some embodiments of the invention,active member 12 can be a polypyrrole film. Such a polypyrrole film maybe synthesized, for example, by electrodeposition according to themethod described by M. Yamaura et al., “Enhancement of ElectricalConductivity of Polypyrrole Film by Stretching: Counter-ion Effect,”Synthetic Metals, vol. 36, pp. 209-224 (1988), which is incorporatedherein by reference. In addition to polypyrrole, any conducting polymerthat exhibits contractile or expansile properties may be used within thescope of the invention. Polyaniline, polysulfone, polyacetylene areexamples.

Electrolyte 14 may be, for example, a liquid, a gel, or a solid, so longas ion movement is allowed. Moreover, where the electrolyte 14 is asolid, it will typically move with the active member 12 and willtypically not be subject to delamination. Where the electrolyte 14 is agel, it may be, for example, an agar or polymethylmethacrylate (PMMA)gel containing a salt dopant. Where the electrolyte is a liquid, it maybe, for example, a phosphate buffer solution, KCl, NaCl and so forth.The electrolyte may be non-toxic in the event that a leak inadvertentlyoccurs in vivo.

Counter electrode 18 is in electrical contact with electrolyte 14 inorder to provide a return path for charge to a source 20 of potentialdifference between member 12 and electrolyte 14. Counter electrode 18may be any suitable electrical conductor, for example, anotherconducting polymer, a conducting polymer gel, or a metal such as gold orplatinum, which can be, for example, in wire or film form and can beapplied, for example, by electroplating, chemical deposition, orprinting. In order to activate actuator 10, a current is passed betweenactive member 12 and counter electrode 18, inducing contraction orexpansion of member 12. Additionally, the actuator may have a flexibleskin for separating the electrolyte from an ambient environment.

The actuator can be provided in an essentially infinite array ofconfigurations as desired, including planar actuator configurations(e.g., with planar active members and counter-electrodes), cylindricalactuator configurations (e.g., see the actuator illustrated in FIG. 5,which is illustrated as having a cylindrical active member and wire coilcounter electrode), and so forth.

Additional information regarding the construction of actuators, theirdesign considerations, and the materials and components that may beemployed therein, can be found, for example, in U.S. Pat. No. 6,249,076,assigned to Massachusetts Institute of Technology, and in Proceedings ofthe SPIE, Vol. 4329 (2001) entitled “Smart Structures and Materials2001: Electroactive Polymer and Actuator Devices (see, in particular,Madden et al, “Polypyrrole actuators: modeling and performance,” at pp.72-83), both of which are hereby incorporated by reference in theirentirety.

One or more actuators 140 can be used to change the deflection angleassociated with the reflective member 136. Moreover, these actuators 140can be associated with the reflective member 136 in a wide range ofconfigurations. For example, in the embodiment illustrated in FIG. 1A,the angle of inflection of the reflective member 136 increases uponlengthwise expansion of the actuator 140, and decreases upon lengthwisecontraction of the actuator 140. For this purpose, an elongated columnof electroactive polymer material can be used in connection with anactuator design like that of FIG. 5.

However, myriad other designs are also possible. For example, anactuator having substantial tensile strength, but negligible columnstrength, can be placed in tension with a reflective member that is inmechanical communication with a spring element. For example, referringagain to the catheter apparatus of FIG. 1A, the hinge 137 can beprovided with a spring element which urges the mirror in acounterclockwise direction. In such an embodiment, as above, the angleof incidence is controlled based on the degree of contraction orexpansion of the actuator 140, with expansion of the actuator 140leading to a greater angle of incidence, and contraction leading to alesser angle of incidence.

As another example, FIG. 6 provides a schematic cross-sectional view ofan electroactive polymer layer stack, which can be used in the formationof an expandable actuator 140. Referring now to FIG. 6, a stack ofcounter-electrode layers 218, active layers 212 andelectrolyte-containing layers 214 are shown. As above, thecounter-electrode layers 218 may be formed from a suitable electricalconductor, for example, a metal such as gold or platinum. Theelectrolyte within the electrolyte-containing layers 214 can be, forexample, a liquid, a gel, or a solid, with appropriate measures beingtaken, where needed, to prevent short-circuiting between thecounter-electrodes 218 and the active layers 212. The active layer 212comprises an electroactive polymer, for example, polypyrrole,polysulfone, polyacetylene or polyaniline. The actively layers 212 canalso optionally be provided with conductive electrical contacts (notshown), if desired, to enhance electrical contact with the controlsystem. During operation, an appropriate potential difference is appliedacross the active layers 212 and the counter-electrode layers 218.Typically, all of the active layers 212 are shorted to one another, asare all of the counter-electrode layers 218, allowing the active layers212 to expand and contract simultaneously. As above, the electroactivepolymer active layers 212 expand and contract upon establishing anappropriate potential difference between the active layers 212 and thecounter-electrode layers 218. This, in turn, expands or contracts theactuator stack.

As another example, electroactive polymer actuators are known in whichan electroactive polymer is laminated between conductive layers toproduce a bending-type actuation, with the degree of bending beingdependent upon on the applied voltage. Such an actuator 140 isillustrated in FIG. 1B, wherein the angle at which the reflective member136 is tilted increases with increasing bend of the actuator 140. Formore information concerning such actuators, see, e.g., Pelrine et al.,Smart Structures and Materials 2001: Electroactive Polymer Actuators andDevices, Yoseph Bar-Cohen, Ed., Proceedings of SPIE Vol. 4329 (5-8 Mar.20001), pp. 335-349, which is hereby incorporated by reference. Thisreference also describes numerous other known electroactive polymerconfigurations, including extender, bowtie, diaphragm, spider, tube, androll configurations, which can be used to change the deflection angle ofa reflective member 136.

In many embodiments, the inclination angle of the reflective member isinferred, for example, from the intrinsic position-dependent electricalproperties of the electroactive polymer actuator. However, one or morestrain gauges may also be employed to provide electronic feedbackregarding the inclination angle of the reflective member. Thiselectronic feedback will also provide a number of additional advantages,including greater stability, error correction, and immunity from drift.Strain gauges suitable for use in the present invention include (a)feedback electroactive polymer elements whose impedance or resistancevaries as a function of the amount of strain in the device, (b) lineardisplacement transducers (e.g., an iron slug slidably positioned in thecore of a coil) and (c) conventional strain gauges in which theresistance of the device varies as a function of the amount of strain inthe device, thus allowing the amount of strain to be readily quantifiedand monitored. Such strain gauges are commercially available from anumber of different sources, including National Instruments Co., Austin,Tex., and include piezoresistive strain gauges (for which resistancevaries nonlinearly with strain) and bonded metallic strain gauges (forwhich resistance typically varies linearly with strain).

Timing and control circuitry is also typically provided in connectionwith the above described catheter apparatus to control, for example, theoperation of the ultrasonic transducer, the actuator, and the motordrive. A display is also typically provided, which is operated under thecontrol of the timing and control circuitry for displaying imageinformation.

In this connection, a schematic block diagram is presented in FIG. 4,which illustrates the electrical components utilized in a cathetersystem, in accordance with one embodiment of the present invention. Aspreviously noted, the entire catheter apparatus, including thetransducer 132, actuator 140, and the coaxial cable 32, rotates as asingle unit in the embodiment described above. Electrical connection cannonetheless be established between these components and a non-rotatingelectrical system using methods known in the art. For example,electrical connections can be made as described in U.S. Pat. No.5,000,185 by using a pair of spaced-apart rotating slip rings 62, 63,which are formed of a conducting material, and which are placed inelectrical connection with the conductive members of the coaxial cable32. A pair of spring-urged contacts, for example, conductive brushes,can be adapted to slidably engage the slip rings, which contacts areconnected to conductors 73 and 74. Alternatively, a rotary transformerfamiliar in the art (not shown) may provide coupling with no movingparts.

Motor 99 is driven by and is under the control of electronic circuitryforming a part of electrical system 101. Such a system 101 includes atiming and control block 102, which supplies pulses to a transmitter103. The output of the transmitter 103 is supplied through atransmit/receive switch 104 which supplies the signals through theconductors 73 and 74, through the slip rings 62 and 63, through theinner and outer conductors of the coaxial cable 32, and to theultrasonic transducer 132 and the actuator 140 as described above.System 101 is capable of supplying high frequency energy to theultrasonic transducer 132 and low frequency/dc energy to the actuator140 via the transmitter 103, while at the same time driving the driveshaft 114 using motor 99, which is also under the control of the timingand control block 102. The motor 99 can be, for example, an open loopstepping motor or a closed drop servo-controlled motor that can bedriven by the timing and control block 102.

As an alternative to the use of an external motor 99, it is alsopossible to construct catheters in accordance with the presentinvention, in which motor(s) are provided within the distal end of thecatheter, allowing the reflective member to be rotated, for example.Also, as indicated above, the catheter can be manually rotated.

Voltage pulses for excitation of the transducer 132 commonly range, forexample, from 10 to 50 volts. The transducer 132 produces ultrasonicwaves which emanate therefrom, reflecting from the surface of thereflective member and into the surrounding tissue as described above.Portions of the ultrasonic sonic energy waves rebounding from the tissueare also reflected from the reflective member and back to the transducer132, whereupon the transducer acts as a receiver, picking up ultrasonicwaves and converting them into electrical signals which are supplied bythe coaxial cable 32, to the slip rings 62 and 63, through theconductors 73 and 74, and through the transmit/receive switch 104 to areceiver 106. These signals are amplified and supplied to a displayunit, which includes a display monitor 108 under the control of thetiming and control block 102 to supply an image on the display 108.

Operation and use of the catheter apparatus and system is brieflydescribed as follows. The catheter apparatus of the present invention isintroduced into a body lumen of a patient, for example, into the femoralartery. In some embodiments, the catheter apparatus can be advanced overa guidewire as is known in the art. The progress of the catheter intothe patient can be observed, for example, under x-ray fluoroscopy. Thevessel wall itself can be viewed by suitable operation of system 101.This can be accomplished, for example, by operating the timing controlblock 102 to cause operation of the motor 99 which in turn causesrotation of the drive shaft. As a result, the transducer 132 andreflective member are allowed to scan the interior of the vessel inwhich the catheter is disposed, typically at a rotation rate whichachieves a “real-time” scan, for example, 30 frames per second (i.e.,1800 frames, or rotations, per minute). Suitable rotation rates are thustypically in the range of 5 to 60 revolutions per second, i.e., 300 to3600 rpm. An image of what is being scanned will appear on the screen108 of the display device. Alternatively, the drive shaft may bemanually rotated (or aimed without rotation) to provide a desired image.Generally, however, motorized rotation will provide a higher definitionimage. As in prior art systems, distinct cross-sectional images aresuccessively produced as the catheter apparatus is advancedincrementally, allowing the operator to determine the length andtopography of the region. In the present invention, however, a portionof the vessel length can also be longitudinally scanned by operating theactuator 140 to tilt the reflective member. As noted above, dependingupon the angle of the reflective member, the scan can constitute aforward scan, a lateral scan, a rearward scan, or a combination of allthree.

In addition to imaging capability, the catheters of the presentinvention may further include interventional capability, for example,for recanalization of occluded regions within the imaged blood vessel,as is known in the art. By recanalization is meant both the opening oftotal occlusions as well as the broadening of the vessel lumen inpartial occlusions. Catheters combining ultrasonic imaging capabilitywith atherectomy devices for severing of the stenotic material aredescribed in detail in U.S. Pat. No. 5,000,185. Of course, the cathetersof the present invention are not limited to use in atherectomy and canbe used to perform a wide variety of other interventional techniquesthat are performed with vascular catheters. Suitable interventionaltechniques include balloon angioplasty, cutting balloons, laser ablationangioplasty, balloon embolectomy, aspiration embolectomy, heat probeablation, abrasion, drilling, therapeutic ultrasound, and the like.Also, the catheters may be adapted for introducing clot-dissolvingdrugs, such as tissue plasminogen activator, streptokinase, orurokinase, in order to reduce the stenosis, as well as anti-restenosisdrug which inhibit restenosis, such as paclitaxel.

Although various embodiments are specifically illustrated and describedherein, it will be appreciated that modifications and variations of thepresent invention are covered by the above teachings and are within thepurview of the appended claims without departing from the spirit andintended scope of the invention.

1. An ultrasonic imaging catheter apparatus comprising: a flexibleelongate body adapted for insertion into a body lumen, the elongate bodyhaving distal and proximal ends; an ultrasonic transducer disposedproximate said distal end of said elongate body, said ultrasonictransducer generating and detecting ultrasonic energy; a reflectivemember proximate said ultrasonic transducer, said reflective memberbeing adapted to reflect (a) ultrasonic energy generated by saidultrasonic transducer to a wall of said body lumen and (b) ultrasonicenergy reflected by said wall back to said transducer; and an actuatorin mechanical communication with said reflective member, said actuatorbeing adapted to change the angle of incidence of said ultrasonic energyrelative to said reflective member.
 2. The ultrasonic imaging catheterapparatus of claim 1, wherein control signals for said ultrasonictransducer and for said actuator are transmitted via a common electricalconductor.
 3. The ultrasonic imaging catheter apparatus of claim 2,wherein said ultrasonic transducer is provided with a high pass filterto block said actuator control signals.
 4. The ultrasonic imagingcatheter apparatus of claim 3, wherein the high pass filter comprises acapacitor.
 5. The ultrasonic imaging catheter apparatus of claim 2,wherein said actuator is provided with a low pass filter to block saidultrasonic transducer control signals.
 6. The ultrasonic imagingcatheter apparatus of claim 5, wherein the low pass filter comprises aninductor.
 7. The ultrasonic imaging catheter apparatus of claim 2,wherein said common electrical conductor is a coaxial cable.
 8. Theultrasonic imaging catheter apparatus of claim 1, wherein said actuatoris an electroactive polymer actuator.
 9. The ultrasonic imaging catheterapparatus of claim 8, wherein said reflective member is rotatable withrespect to an axis of said body lumen
 10. The ultrasonic imagingcatheter apparatus of claim 9, wherein said ultrasonic transducer isrotatable with respect to said axis of said body lumen.
 11. Theultrasonic imaging catheter apparatus of claim 9, further comprising arotatable housing, wherein said reflective member and said electroactivepolymer actuator are mounted within said housing.
 12. The ultrasonicimaging catheter apparatus of claim 11, wherein the housing comprises amaterial that is substantially transparent to said ultrasonic energy.13. The ultrasonic imaging catheter apparatus of claim 11, wherein saidreflective member is provided with a mechanical hinge, wherein saidmechanical hinge is secured to said housing, and wherein saidelectroactive polymer actuator is disposed between said housing and saidreflective member.
 14. The ultrasonic imaging catheter apparatus ofclaim 1, wherein said reflective member is provided with a mechanicalhinge.
 15. The ultrasonic imaging catheter apparatus of claim 8, whereinsaid electroactive polymer actuator comprises an electroactive polymerregion, a counter-electrode region, and an electrolyte-containing regiondisposed between said electroactive polymer region and saidcounter-electrode region.
 16. The ultrasonic imaging catheter apparatusof claim 8, wherein said electroactive polymer actuator comprises anelectroactive polymer selected from polyaniline, polysulfone,polyacetylene and polypyrrole.
 17. The ultrasonic imaging catheterapparatus of claim 9, further comprising a motor and a drive shaft, saiddrive shaft translating torque from said motor to rotate said reflectivemember.
 18. The ultrasonic imaging catheter apparatus of claim 8,comprising a plurality of electroactive polymer actuators, wherein saidplurality of electroactive polymer actuators are adapted to change theangle of incidence of said ultrasonic energy relative to said reflectivemember.
 19. A method of scanning the inner wall of a body lumencomprising: providing the catheter apparatus of claim 9, sweeping saidultrasonic energy in a predetermined pattern over the interior wall ofthe body lumen, wherein said sweeping is accomplished by rotating saidreflective member and operating said electroactive polymer actuator tochange the angle of incidence of said ultrasonic energy relative to saidreflective member; receiving ultrasonic energy reflected from theinterior wall of the body lumen; and producing an image from thereflected ultrasonic energy.
 20. The method of claim 19, wherein theultrasonic energy is directed at a forward angle of from about 10° toabout 85° relative to the axis of the body lumen, whereby a forwardconical sweep is performed.
 21. The method of claim 19, furthercomprising axially advancing the reflective member within the bodylumen.
 22. The method of claim 19, wherein the reflective member isrotated under electronic control.